1) Field of the Invention
The present invention relates to a communication terminal that builds a wireless network and a communication method by which the communication terminal performs a communication, and more particularly, to a communication terminal and a communication method capable of efficiently optimizing a data transmission route even under a situation in which a communication terminal moves or a new communication terminal is connected to the wireless network.
2) Description of the Related Art
A technology for data transmission or data reception through an ad hock network is widely known. The ad hock network is one of wireless networks and is not dependent on infrastructure such as base stations. The ad hock network is built by communication terminals mutually connected wirelessly.
Each of the communication terminals connected to the ad hock network includes a function of relaying data for the other destination communication terminals. Therefore, even if a distance up to a communication terminal as a destination of data is such a long distance that radio waves do not reach and data is impossible to be directly transmitted, the data is relayed through some communication terminals, which makes it possible to transmit the data to the communication terminal as a destination.
In the technology, when a communication terminal is to transmit data, a communication route up to a destination communication terminal needs to be ensured. Therefore, the communication terminal that is to transmit data transmits control information to other unspecified communication terminals. A communication terminal receives the control information, enters information for a data transmission route between a source communication terminal and its own (local) communication terminal in the control information, and transmits the control information to other unspecified communication terminals.
When control information is transmitted one after another between communication terminals and the control information reaches a destination communication terminal, a data transmission route from a source communication terminal to a destination communication terminal is built, and data is transmitted based on transmission route information entered in the control information.
In the ad hock network, however, a communication terminal included in the data transmission route may be disconnected from the ad hock network because the communication terminal deviates from a range where radio communication is possible or the power is shut off, which may cause data communication to be impossible. In this case, in the conventional technology represented in Japanese Patent Application Laid-Open No. 2000-252992, if it is detected that the data cannot be transmitted, the control information is transmitted again to ensure a new transmission route.
In the conventional technology, however, even if a destination communication terminal moves to allow data transmission to be possible through the less number of times of relay, the data transmission route cannot be updated if the transmission route having been once ensured can still be used. Japanese Patent Application Laid-Open No. 2000-341323 discloses a wireless ad hock terminal that periodically transmits control information between a relay communication terminal that performs relay and a destination communication terminal, and that establishes a connection with a relay communication terminal near the location to which the destination communication terminal has moved.
However, in the conventional technology disclosed in Japanese Patent Application Laid-Open No. 2000-341323, updating a communication route based on control information periodically transmitted is performed only between a destination communication terminal and a final relay communication terminal that relays data to the destination communication terminal, and therefore, another transmission route cannot be optimized.
More specifically, in the ad hock network, not only a destination communication terminal but also a relay communication terminal freely moves. Even if an effective transmission route with the less number of times of relay becomes available as a result of movement of the relay communication terminal, this transmission route cannot be used.
If a new communication terminal is connected to the ad hock network, a data transmission route with the less number of times of relay may be available, but such a transmission route cannot effectively be searched for.